1. Field of the Disclosure
The technology of the disclosure relates to optical interfaces in fiber optic connector assemblies for establishing fiber optic connections.
2. Technical Background
Benefits of optical fiber include extremely wide bandwidth and low noise operation. Because of these advantages, optical fiber is increasingly being used for a variety of applications, including but not limited to broadband voice, video, and data transmission. Fiber optic networks employing optical fiber are being developed and used to deliver voice, video, and data transmissions to subscribers over both private and public networks. These fiber optic networks often include separated connection points linking optical fibers to provide “live fiber” from one connection point to another connection point. In this regard, fiber optic equipment is located in data distribution centers or central offices to support optical fiber interconnections.
Optical fibers may also be used to connect optical devices to the fiber optic networks. In applications for optical devices where high bandwidth and electrical coupling is desired, hybrid fiber optic cables may be employed. Hybrid fiber optic cables include one or more optical fibers capable of transporting optical signals optically at high bandwidths. Hybrid cables may also include one or more electrical conductors capable of carrying electrical signals, such as power as an example. These hybrid cables may be employed in devices, such as user devices used by consumers, to provide optical and electrical signal connectivity.
It is common to provide a flat end-faced multi-fiber ferrule to more easily facilitate multiple optical fiber connections between the fiber optic connector including the ferrule and another optical device, for example, another fiber optic connector or optical fiber. In this regard, it is important that the fiber optic connector be designed to allow end faces of the optical fibers disposed in the ferrule to be placed into contact or closely spaced with respect to the other optical device for light transfer. If an air gap is disposed between the optical fiber held in the ferrule and the other optical device, the end of the optical fiber is cleaved (e.g., laser-cleaved) and polished into a curved form to allow it to act as a lens in an effort to reduce optical attenuation. However, spherical aberrations can occur when the end face of the optical fiber is cleaved and polished into a curved form thereby introducing further optical losses.
Gradient index (GRIN) lenses offer an alternative to polishing curvatures onto ends of optical fibers to form lenses. GRIN lenses focus light through a precisely controlled radial variation of the lens material's index of refraction from the optical axis, typically at the center axis, to the edge of the lens. The internal structure of this index gradient can dramatically reduce the need for tightly controlled surface curvatures and results in a simple, compact lens. This allows a GRIN lens with flat surfaces to collimate light emitted from an optical fiber or to focus an incident beam into an optical fiber. The GRIN lens can be provided in the form of a glass rod that is disposed in a lens holder as part of a fiber optic connector. The flat surfaces of a GRIN lens allow easy bonding or fusing of one end to an optical fiber disposed inside the fiber optic connector with the other end of the GRIN lens disposed on the ferrule end face. The flat surface on the end face of a GRIN lens can reduce aberrations, because the end faces can be polished to be planar or substantially planar to the end face of the ferrule. The flat surface of the GRIN lens allows for easy cleaning of end faces of the GRIN lens. It is important that the GRIN lens be placed and secured in alignment with the desired angular accuracy to avoid or reduce coupling loss.
It is common for each GRIN lens of a plug or receptacle to be placed and secured in optical connectors by a ferrule, which also directly secures the optical fiber to which the GRIN lenses are attached. However, the GRIN lenses may be challenging to position precisely within the ferrule without specialized and expensive equipment because GRIN lenses may be relatively small, for example, no more than one (1) millimeter in length. If the GRIN lens is imprecisely positioned within the ferrule, then the ferrule including the GRIN lens may have to be discarded, resulting in additional manufacturing expense as both the GRIN lens and combination ferrule assembly may have to be replaced.
Moreover, adding additional features to the ferrule to more precisely position the GRIN lenses makes the ferrule prohibitively expensive to build for consumer markets and increases the size of the optical connector to accommodate the ferrule. The allowable size of optical connectors of the plug and receptacle are limited given the trend for user devices having smaller sizes to enable mobility and having commensurately small interconnecting interfaces.
New approaches are needed for the design of fiber optic connectors, including GRIN lenses, to more reliably and efficiently align the GRIN lenses of plugs to optical fibers leading up to the plugs and complementary GRIN lenses on receptacles. The new approaches may also be compatible for hybrid optical connectors establishing electrical coupling and optical connections for optical devices.